Extract preparation and chromatin immunoprecipitation were performed as in Kolasinska-Zwierz et al. (2009) with the following modifications: tissue was fixed for 10 min in 1.5 mM EGS (Pierce 21565) then formaldehyde added to 1% for a further 10 min before quenching with 0.125M glycine and washing 2X with PBS plus protease inhibitors. Pellets were washed once in FA buffer, then resuspended in 1 ml FA buffer per 1 mL of ground worm powder and the extract sonicated to an average size of 250 base pairs with a Diagenode Bioruptor or Bioruptor Pico for 28 pulses of 30 s followed by 30 s pause. Following ChIP and DNA purification, libraries were prepared using the Illumina TruSeq kit. Fragments in the 250–300 base pair range were selected using Agencourt AMPure XP beads. Two biological replicate ChIPs were conducted for each factor.